A waveguide converter is a converter placed between a waveguide which is a microwave transmission line and a planar line like a strip line which is also the microwave transmission line. For example, it is used widely when an antenna or a waveguide is connected to a high-frequency wave circuit. The reason is that a waveguide which is a hollow metal tube is generally used for input and output with the outside of a wireless communication device, while a distributed constant line or a coaxial line like a micro-strip line is generally used in a high-frequency wave circuit within the wireless communication device. That is because a converter which performs mode conversion is required for connection between two kinds of microwave transmission lines each having a different transmission mode. Examples of such waveguide converters are described in following Patent Literatures 1 to 3.
For example, Patent Literature 1 (i.e. PTL 1) describes a related waveguide converter in which a probe is arranged in a direction parallel to an electric field of microwaves transmitting in a waveguide and a movable screw 78 which adjusts a distance from the probe to a short-circuit face of the waveguide is placed, as shown in FIG. 8A and FIG. 8B. FIG. 8A is a top view of the waveguide converter and FIG. 8B is a cross-sectional view of the waveguide converter. A reference label “D” in FIG. 8B indicates the distance from a probe 25 to the short-circuit face of a waveguide 20. In the related waveguide converter, setting of a length and a thickness of the probe and adjustment of the distance by the movable screw enables to make impedance matching between the waveguide and an amplifier.
Patent Literature 2 (i.e. PTL 2) describes a waveguide converter with another structure in which a strip antenna is mounted on a substrate, a short-circuit mechanism portion in which an elliptic concave portion whose height is equivalent to a width of an inner shape of a waveguide is formed in a carrier which is located on a back of the antenna, and an adjustment screw 79 is placed in a center of the elliptic concave portion, as shown in FIG. 9A and FIG. 9B. FIG. 9A is a top view illustrating another structure of the waveguide converter, and FIG. 9B is a cross-sectional view illustrating another structure of the waveguide converter. In the related waveguide converter, manufacturing of the short-circuit mechanism portion and setting of an electrical length are easily performed. Patent Literature 3 (i.e. PTL 3) describes a related waveguide and a micro-strip line converter. In the PTL 3, a male screw is provided on an adjusting plate internally fitted in the waveguide, and a setscrew for fixing a spacer and the adjusting plate is combined. Thereby, a position adjusting portion of the adjusting plate of the waveguide terminating portion can be made smaller than an outer diameter of a chassis.